Nothofagus pumilio dieback in Northern Patagonia: The influence of climate variations

MILAGROS RODRIGUEZ, SALVADOR CALÍ Y RICARDO VILLALBA

Bariloche

Congreso; VI Southern Connection Congress; 2010

Southern Connection

<!-- @page { margin: 2cm } P { margin-bottom: 0.21cm } -->The aim of this study is to determine the climatic influences onNothofagus pumilioforest diebackin Patagonia. Two Increment cores were collected from 50 individuals at Taraya (39°06´S, 71°09´W) and Paso Córdoba (40°53´S, 70°50´W). Tree positions were recorded to evaluate changes in tree growth related to endogenous dynamics. Crown mortality, dead bark at breast height, Mysodendron abundance, insect and woodpecker damages were also quantified. Samples were processed using traditional dendrochronological techniques. Both visual and computer-assisted cross dating were used to date the cores. Ring widths were standardized using a horizontal line through the mean. Dominant patterns of tree growth were identified using Principal Component analysis. Similar patterns were observed in both sites. An old and a young cohort of trees were identified at the Taraya stand. Although most old trees show a steady reduction in tree growth since the 1940s, a few dominant trees increase growth in the past decades. The cohort of young trees has a positive growing trend and no dieback. Most large trees in Paso Córdoba show a reduction in radial growth from early 1940s. A second group increased the growth rate in the 1940s and stabilized during the recent 6 decades. The release of resources by the declining trees has accelerated the rate of growth of the remaining trees in the stand. At both sites, major changes in growth pattern are related to extreme drought events as those recorded in 1943-44